1. Technical Field
The present invention relates to a lane keeping control device of a vehicle that drives an electric power steering motor to travel along a set target course.
2. Related Art
In recent years, for the purpose of reducing traffic accidents and burdens on drivers, various techniques have been developed and proposed for lane keeping control devices that support, assist, and control steering so that vehicles can travel along a set target course. For instance, Japanese Unexamined Patent Application Publication (JP-A) No. 2007-326534 discloses a technique for a vehicular lane keeping support device that detects lateral displacement from the vicinity of a lane center of a vehicle on the basis of lane shape information obtained by an image captured by a camera and calculates, on the basis of the detected lateral displacement, reference steering torque to be applied to the vehicle to enable the vehicle to travel along the lane. According to the technique, steering torque to be applied to the vehicle is changed from the reference steering torque by increasing a dead zone or reducing a gain of the steering torque with respect to the lateral displacement when a lane width of a road is large compared with when the lane width is small.
When a driver travels on a road, as illustrated in FIG. 8A, if the driver travels on a traveling road having a large traveling road width (Wr>C: Wr represents traveling road width and C represents reference width set in advance) like an expressway, it is possible to assist steering of the driver and perform natural and stable lane keeping control along a target course by performing feedback control to eliminate a deviation from a target course set on the traveling road (e.g., the center of the traveling road). On the other hand, as illustrated in FIG. 8B, if the driver travels on a traveling road having a small traveling road width (Wr<C) like a general road, obstacles such as parked vehicles and oncoming vehicles are often present on the traveling road. The driver needs to travel while avoiding the obstacles. The driver has a lot of difficulties in traveling a target course on the traveling road. Taking into account such actual traveling environments, the lane keeping control device disclosed in JP-A No. 2007-326534 attempts to improve lateral position retaining performance in a lane by intensifying control when a road width decreases. Then, on the contrary, the lane keeping control for traveling along the target course prevents the steering of the driver.